The human body includes arterial and venous conduits which run throughout various sections of the human body. These conduits conduct blood into and from the heart which maintain the circulation that helps to sustain the metabolic events in the body. The vessels undergo biological, physiological and mechanical changes depending on the body metabolism which determine the functionality of the wall of the artery.
Sometimes the wall of an artery becomes occluded due to deposits of fatty tissues which in turn form plaque on the walls of the artery. These plaques then have to removed to restore the normal function of the artery. One known mechanism of removing the plaque is to compress the plaque against the wall of the artery using a balloon catheter. This procedure is called Percutaneous (under the skin) Transluminal (under x-ray guidance) Coronary (region of intervention) Angioplasty (plaque compression) or PTCA.
For a PTCA procedure to be accomplished, a balloon catheter and a guidewire along with a guiding catheter are typically required. The guiding catheter is normally introduced in a groin artery and pushed upwards towards the aorta until it reaches the mouth of the coronary artery. Once the guiding catheter is placed at the opening of the coronary artery, a highly floppy wire is introduced into the guiding catheter such that the wire crosses the mouth of the guiding catheter and goes into the coronary artery. It then has to reach the site of the lesion (plaque) which is usually a very tortuous route and the operator (the cardiologist) has to struggle to reach the guidewire in place. Once a guidewire has crossed the lesion, it is then pushed distally to the lesion so that it remains at a safe place. This is to ensure that the wire does not slip out of the lesion.
A catheter which has a balloon at one end and a shaft at the other end is usually introduced into the lesion on top of the guidewire. Although the mechanism of introduction and the design of the catheter that facilitate the mechanism have been improved by known catheters, they still leave room for improvement.
Several designs of balloon catheters are disclosed in various U.S. patents that facilitate insertion into the artery using a guidewire as an intermediate tool. The way in which the balloon travels on top of the guidewire and the length of the catheter that travels on top of the guidewire is the subject of known devices such as those shown and described in U.S. Pat. Nos. 5,620,417; 5,607,406; 5,607,394; 5,598,844; 5,549,556; 5,545,134; 5,531,690; 5,514,092; 5,077,311; 5,501,227; 5,489,271; 5,472,425; 5,468,225; 5,460,185; 5,458,613; 5,443,457; 5,413,560; 5,413,559; 5,409,097; 5,387,226; 5,383,853; 5,380,283; 5,357,978; 5,336,184; 5,334,147; 5,195,978; 5,170,286; 4,748,982; 4,762,129; and 5,626,600, all of which are incorporated herein in their entirety.
While each one of these above-listed patents describe and illustrate several ways of approaching the traverse mechanism, all of them essentially assume the following; (1) the catheter has proximal and distal ends; (2) there is a balloon mounted on the distal end; (3) the proximal end has a shaft; (4) the interior of the balloon is in communication with a lumen; (5) there is another sleeve that either extends towards the entire length of the catheter or runs at a fixed distance from the distal end of the catheter; (6) the sleeve if it does not run the entire length of the catheter extends up to a predetermined distance from the balloon up to the midsection of 1/3 of the entire catheter length or sometimes shorter; (7) the portion of the sleeve is called the flexible portion, while the proximal portion is either a hallow tube or an elliptical structure which provides for pushability of the catheter; (8) the sleeve has one opening at the proximal side of the balloon through which a guidewire can be inserted and it comes out through the center of the balloon--this is commercially known as the rapid exchange or the monorail concept; (9) in instances where the sleeve extends along the entire length of the balloon the wire extends inside the sleeve from the distal to the proximal end of the catheter through the balloon--this is called the over the wire concept.
In the devices of the above patents, regardless of whether the catheter is over the wire or monorail, the guidewire has one entry point and one exit point and the regions between the entry and exit are imbedded in the catheter sleeve or the catheter shaft.
However, the catheters of the above patents have some serious disadvantages in lesions that are completely occluded or in lesions that have severe tortuosity. In lesions that have complex distal diseases the catheter has to traverse multiple bifurcations in order to reach the site of lesion. In case of the above described known catheters, the operator or the cardiologist forces the body of the catheter on top of the wire using an external force. This force then transmits from the catheter body to the surface of the wire. When the wire is held with a counteractive force, the force against the catheter becomes greater and a law of physics comes into play, the object with the greatest force moves forward.
In balloon angioplasty, it is desired to design a catheter which pushes on top of a wire with a minimum force. In order to achieve this, catheters with very low profiles are sought. These low profiles enable easy slippage on top of the wire. Sometimes the wires are also coated with a lubricous coating to enable ease of passage of the catheter.
In numerous instances, the operator is unable to cross a lesion with a rapid exchange catheter. He then switches over to an over the wire design or vice versa when the operator cannot transmit the necessary force for the balloon catheter to traverse the lesion.
In general rapid exchange catheter designs are preferred because there is only about 1/3 of the catheter body that is imbedded in the guidewire and hence the force required for the catheter to travel is less. In the case of total occlusions, over the wire designs are preferred as the catheter. If the catheter is being pushed through a very hard plaque or a totally occluded artery, the maximum force from the proximal end of the catheter has been delivered to the distal end.
The force delivered at the proximal end by the operator relates to the force of balloon moving forward toward the lesion. There are forces lost between the proximal end to the distal end of the catheter and this happens due to the tortuosity of the lesions, length of the shaft of the catheter and also lesion morphology.
Prior art inventions are easily understood if we draw a very simple analogy between the catheter and the guidewire. Assume the guidewire is the track of the train, and the catheter is the train. In the rapid exchange design, the train has one pair of small wheels that are the distal 1/3 of the catheter of the length of the sleeve. In the case of an over the wire design, the train has one pair of long wheels from the distal end of the catheter to the proximal end.